3D-printed femurs may enhance biomechanical studies

Researchers at UT Southwestern Medical Center have developed a breakthrough three-dimensional (3D) printing technique for generating realistic models of the human femur that could make it easier and less expensive to conduct biomechanical research.

The study, published in the Journal of Orthopaedic Research in collaboration with researchers at The University of Texas at Dallas, is the first to validate the use in biomechanical studies of femurs produced using cost-efficient 3D printers and materials. Though the study focused on replicating the femur (thigh bone) and its unique mechanical properties, the process could be used in the future to build models of any human bone for research.

“The femur is a focal point of biomechanical research because of its critical role in weight-bearing and mobility,” said lead author Robert Weinschenk, M.D., Assistant Professor of Orthopedic Surgery and Biomedical Engineering at UT Southwestern.

“Traditionally, biomechanical researchers have used cadaver or synthetic bones for studies, but those can be expensive, difficult to obtain, and have inherent limitations. The use of 3D printing to generate humanlike bones can be a significant boost to researchers studying new surgical techniques and conditions such as osteoporosis, traumatic fractures, deformities, and benign or malignant bone lesions.”

Collaborating with mechanical engineers from UT Dallas, Dr. Weinschenk and the team used polylactic acid—an inexpensive, biodegradable polyester material commonly used in 3D printing—to construct a wide range of femur models with different physical attributes such as wall thickness and infill density. Those models were then tested for flexural strength using three-point bending, and the results were compared to the biomechanical response of human femurs, enabling the team to identify the methodology that produced the most accurate replica.

Kishore Mysore Nagaraja, a Ph.D. candidate at UT Dallas, developed numerous samples of the printed femurs and tested them to ensure they were mechanically equivalent to actual femur bones.

Four generations of synthetic femur models have been developed for biomechanical testing and sold commercially since 1987, Dr. Weinschenk said. However, they have had limitations, including cost and delivery time. He said the 3D printing technique he and his colleagues created solves those problems.

“We think this is novel and can gain wide use and acceptance because anyone with a cheap 3D printer can download the file, print the specimen, and do their own studies in an inexpensive way without delay,” Dr. Weinschenk said.

The femur is the strongest and longest bone in the human body, with the average adult femur measuring about 18 inches in length. Dr. Weinschenk and his UT Southwestern and UT Dallas colleagues made models of the middle portion of the femur, just under 8 inches in size and almost an inch in diameter. The specimens are produced at an estimated cost of $7.

Researchers at UT Dallas focused on the mechanical evaluation and characterization of the 3D-printed femur.

“With 3D printing, we’re able to print out the femur bone with the same geometry of the femur inside the body,” said Dr. Wei Li, Ph.D., Assistant Professor of Mechanical Engineering at UT Dallas and the study’s senior author. “In our biomechanical tests, the femur performed as well as a human femur.”

Dr. Weinschenk, who specializes in musculoskeletal oncology, and study co-author Richard Samade, M.D., Ph.D., Assistant Professor of Orthopaedic Surgery, Biomedical Engineering, and Plastic Surgery at UTSW, envision researchers soon being able to print patients’ tumors on 3D bones to help personalize their treatment.

“The ability to use a 3D printer to create biomechanically realistic models removes a major obstacle to research and opens the door to clinical applications,” Dr. Samade said.

“For example, a surgeon could print bones with patient-specific pathologies and use those models to develop personalized treatment protocols. It’s a major step forward in engineering surgical solutions for patients with difficult bone pathologies, with a focus on preservation of limb and function.”

Dr. Weinschenk added, “There has been a substantial amount of surgical innovation with regard to orthopedic oncology in the past couple of years—new implants, minimally invasive surgical techniques, etc. Since patients are living longer, we need to keep pace with this innovation and develop improved surgical solutions that will last longer.”

The next step will be coming up with 3D design protocols for a wider range of bone models.

“Once we can print 3D models with confidence that they will behave mechanically like actual bones, we could see a rapid evolution of biomechanical studies that will eventually lead to innovative surgical techniques across orthopedics,” Dr. Weinschenk said. “This study lays the groundwork for our future work here and in collaboration with our colleagues at UT Dallas.”